Relating to conveying and separation apparatus

ABSTRACT

An air distribution plate for incorporation into a material conveyor or a material separator has a plurality of apertured zones alternately arranged along the length of the plate. The apertures in the first series of zones are inclined in the direction of the desired flow of material in the case of the conveyor and in the direction of the desired air flow in the case of the separator and the apertures in the second series of zones incline in the opposite direction by the same amount. Each zone in the second series of zones has fewer apertures than the zones of the first series of zones.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a distribution plate for use inconveying and separation apparatus.

2. Description of the Art

There are a number of known forms of apparatus which are used for theconveying and/or separation of material such as, for example, tobaccoleaf and stem, tea, cereal and other bulk material, using an air stream.

W089/04802 describes both a conveying apparatus and also an apparatusfor separating different grades of a material. Both forms of apparatususe a distribution plate which has a plurality of apertures throughwhich a fluid such as air can flow. The distribution plate is adapted todirect the fluid therethrough in a direction which has a componentextending along a surface of the plate as a result of which materialdisposed above the plate is fluidized and conveyed along the surface ofthe plate.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a distribution plate for aconveying or separating apparatus of the type in which material isconveyed by or separated by an air stream. The distribution plate has aplurality of apertures for directing fluid flow therethrough in adirection which has a component extending along a surface of the plateand wherein the apertures extend through the plate at respective anglesto the surface of the plate in the range of substantially 65° to 85°.

Advantageously, selected apertures extend at different angles to thesurface of the plate with respect to selected other apertures.

Advantageously at least some of said apertures are at an angle of 70° tothe surface of the plate.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 shows in diagrammatic form a side view of one example of aconveying apparatus incorporating a distribution plate in accordancewith the invention;

FIG. 2 is a cross sectional view laterally through the apparatus of FIG.1;

FIG. 3 is a plan view of part of the apparatus of FIG. 1;

FIG. 4 shows to an enlarged scale the detail of the part of theapparatus shown in FIG. 3;

FIG. 5 shows a modified form of the part of the apparatus shown in FIG.3;

FIG. 6 is a diagrammatic side elevation of a separating apparatusincorporating a distribution plate in accordance with the invention; and

FIG. 7 is a cross sectional view of part of the apparatus seen in FIG.6.

FIG. 8 is a cross-sectional view showing apertures extending through adistribution plate at an angle in a range of substantially 65° to 85° tothe surface of the distribution plate, where selected apertures extendin different directions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 and 2, the conveying apparatus comprises aconveying trough 10 having a base wall defined by a distribution plate11 and side walls 12. The trough 10 is closed by a loose fitting cover13. The base wall of the trough 10 may comprise in section, a centralflat portion and side portions which incline upwardly and outwardly tothe lower edges of the side walls 12 and furthermore, the side walls 12may incline inwardly by a small amount. A feed hopper 14 is located atthe inlet end of the apparatus and material fed to the hopper 14 fallsdown an inclined member and is deposited onto the distribution plate 11.Beneath the conveying trough 10 there is formed a first plenum chamber15 to which air is supplied by means of a fan 16, the air passingthrough apertures to be described in the distribution plate 11 into theconveying trough 10. The air leaves the trough 10 through apertures inthe side walls 12 thereof and flows into a pair of second plenumchambers 17 and is conveyed back towards the fan 16 for recirculation.In use, materials, such as tobacco, is loaded into the hopper 14 and isconveyed, as will be explained, along the trough 10 to the outlet end ofthe apparatus.

The distribution plate 11 will now be described with reference to FIGS.3 and 4. The arrow A indicates the direction of flow of the materialalong the trough 10 and it will be seen that the plate 11 is formed soas to define two series of zones 18, 19 of apertures or holes. The zones18, 19 are alternately arranged with spaces 19A between adjacent zones,in which there are no holes. The zones 18, 19 of holes may be formed inindividual plates which are assembled to form the base wall of thetrough 10 however, it is preferred that the distribution plate 11 is aone piece item extending, if possible, the length of the apparatus.

In the zones 18 which are of a length considered in the direction of thearrow A longer than the zones 19, the holes 18H are angled in thedirection A but in the zones 19 the holes 19H are angled in the oppositedirection, as shown in FIG. 8. The material forming the distributionplate 11 is conveniently stainless steel sheet and the holes arechemically etched therein. The holes are angled in the range 65°-85°,preferably 70°, to the surface of the plate 11 so that the air leavingthe holes has a similar angle to the surface of the plate 11.

The air flow through each hole has a component normal to the surface ofthe plate 11 and a further component parallel to the surface of theplate 11 and extending in the direction A or in the opposite directiondepending upon the zone in which the particular hole is situated. Thecomponents of the air flow which are normal to the plate 11 lift thematerial clear of the surface of the plate 11 by an amount which dependsupon a number of factors such as, for example, the air pressure in thefirst plenum chamber 15 and the size of the holes. The component of theair flow which extends parallel to the surface of the plate 11 and whichissues from the holes in the zones 18 moves the material along thetrough 10. If the holes in the plate 11 were all angled in the samedirection A, the material supplied to the trough 10 from the hopper 14would tend to accelerate as it moved along the trough 10 since the forceacting on the material in the trough 10 due to the components of airflow parallel to the surface of the plate 11 is cumulative. It ispossible to provide a zone of appreciable length at the end of thetrough 10, in which the air flow through the holes in that zone is suchas to decelerate the material flowing along the trough 10, however, byproviding the intervening zones 19 the rate of flow of the material iscontrolled throughout the length of the trough 10. Since the zones 19are shorter in length than the zones 18, the material does move alongthe trough 10 in the direction of arrow A as the resultant force factorextends in the direction of the arrow A.

In a specific example, the holes are angled at substantially 70°however, holes lying in the range 65°-85° can also be used. Thestainless steel sheet forming the plate 11 has a nominal thickness of0.71 mm, the hole size is approximately 1.0 mm and there areapproximately 1.8 holes per square centimeter.

The side walls 12 of the trough 10 are also provided with holesindicated at 20 in FIG. 2 to permit air to pass into the second plenumchambers 17. The holes 20 are arranged normal to the surfaces of theside walls 12 and conveniently the holes are shaped to provide a smallentry aperture for the air and a larger exit aperture into therespective second plenum chamber 17.

In a first modification to the arrangement of the zones, the zones 19Ain which there are no holes are omitted.

A second modification to the arrangement of the holes in thedistribution plate 11 is shown in FIG. 5 in which the zones 18 and 19 ofthe previously described arrangement are replaced by diagonal zones 21,22. In the zones 21 the holes are angled in the direction of the arrow Ato achieve motion of the material supplied to the trough 10 in thedesired direction. In the zones 22 the holes are angled in the oppositedirection and the practical effect of this arrangement is to achieve aneven more uniform flow of the material along the trough 10.

With reference now to FIGS. 6 and 7 there is shown a separatingapparatus having a separation chamber 23 to which material such as, forexample, tobacco leaf and stem can be supplied by means of a beltconveyor 24. Instead of a belt conveyor, a conveyor of the typedescribed above can be used. The upper portion of the chamber 23communicates with an outlet duct 25 and the lower wall of the chamber 23is defined by a pair of inclined distribution plates 26 which are spacedat their lower ends to define an outlet 27 beneath which is arranged aconveyor 28. The side walls of the outlet 27 are formed by plates 33,respectively, in which are formed holes which incline upwardly atsubstantially a 45° angle. Air under pressure is supplied through theholes in the plates 33 from plenum chambers 34. The distribution plates26 are provided with holes through which air can flow into theseparation chamber 23 from plenum chambers 29 respectively. The air issupplied to the plenum chambers 29 through a conduit 30 by means of afan 31 which draws air from the outlet duct 25. The conduit 30 leadsinto a diffuser section 35 which incorporates baffles to provide thedesired air flow to the plenum chambers 29 and 34.

The distribution plates 26 are provided with holes in the same manner asthe plates 11 described above with reference to the conveyor or trough10. The air flowing through the holes in the plates 26 forms twoupwardly flowing outer air streams the velocity of which can becontrolled, for example, by controlling the speed of the fan 31 and theair flowing through the holes in the plates 33 forms a central airstream and the air flowing through the holes in the plates 33 forms acentral upwardly flowing air stream. The velocity of the air stream isadjusted, in such a manner that the components of the material, whichhave a so called lower terminal velocity than the velocity of the airstream, are discharged through the outlet duct 25. The components of thematerial having a higher terminal velocity fall through the outlet 27onto the conveyor 28. In some cases, it is desired to modify the upwardflow of air in the separation chamber 23 and this can be achieved byproviding valves controlled by pass ducts 29A which connect the plenumchambers 29 respectively to the outlet duct 25. By adjusting the valvesthe vertical air flow in the separation chamber 23 can be modified.

The air in the apparatus is recirculated by the fan 31 and a separationunit 32 of known form is provided in the outlet duct 25 and thiscollects those components of the material fed into the separation zonewhich have the lower terminal velocity. The collected material is ledaway from the separation unit 32 by means of a conveyor 32A which can bea belt conveyor or a conveyor of the type described above with referenceto FIGS. 1 and 2. The separation unit 32 will not retain dust and thiswill be recirculated by the fan 31. In order to prevent build up of thedust a proportion of the air delivered by the fan 31 is removed by anextractor 36 unit which filters the air. The air which is withdrawn hasto be replaced and this is conveniently effected by a pair of boosterfans 37 which deliver air more or less directly into the plenum chambers29 respectively. By careful control of the fans 37 the air pressure inthe separation chamber 23 can be arranged so that it is substantiallyatmospheric and, as a result, there is no need to provide an air lock atthe entrance of the conveyor 24 into the separation chamber 23.

The holes in the plates 26 are arranged in the same way as are the holesin the distribution plates 11 of the conveyor or trough 10. In a typicalexample, the plate 26 is 0.71 mm thick, the hole size 1.0 mm and thereare 18.8 holes per square centimeter. The plates 26 are positioned atsubstantially 45° and by using holes at 70° in the configurationsdescribed, the air flow in the outer zones in the separation chamber 23is substantially vertical. This is because the air flow in theseparation chamber 23 produced by the holes which extend upwardly would,without the provision of the holes extending in the opposite direction,progressively incline towards the plate 26 in other words towards thesides of the separation chamber 23. The ratio of the holes in the zones18 and 21 to the holes in the zones 19 and 22 is substantially 3:1.

In the case of the separating apparatus where the conveyors 24 and 32Aare of the type described with reference to FIGS. 1 and 2, the supply ofair thereto may be delivered from the conduit 30 in the case of theconveyor 32A and from one of the plenum chambers 29 in the case of theconveyor 24.

I claim:
 1. A distribution plate for a separating apparatus of the typein which first and second materials are separated by air stream, whereinthe first material has a lower terminal velocity than the air stream andthe second material has a higher terminal velocity than the air stream,the distribution plate having a plurality of apertures formed thereinfor directing fluid flow therethrough in a direction which has acomponent extending along a surface of the distribution plate andwherein the apertures extend through the distribution plate at an anglein a range of substantially 65° to 85° to the surface of thedistribution plate, wherein the apertures are arranged in a first seriesof zones spaced along the length of the distribution plate, eachadjacent pair of zones of the first series being separated by a furtherzone forming a second series of zones, the apertures in the first andsecond series of zones being inclined in opposite directions to thesurface of the distribution plate and there being a greater number ofapertures in the first series of zones than in the second series ofzones, such that the fluid flow carries the first material in thedirection of the component extending along the surface of thedistribution plate to separate the first material from the secondmaterial.
 2. The distribution plate according to claim 1 in which theangle of the apertures is substantially 70°.
 3. The distribution plateaccording to claim 1 in which the ratio of the number of apertures ineach one of the first series of zones to the number of apertures in eachone of the second series of zones is substantially 3:1.
 4. Thedistribution plate according to claim 1 in which the first and secondseries of zones extend transversely of the length of the distributionplate.
 5. The distribution plate according to claim 4 in which each ofthe second series of zones is spaced from the adjacent zones of thefirst series of zones by a space in which there are no apertures.
 6. Thedistribution plate according to claim 1 in which the first and secondseries of zones extend diagonally to the length of the distributionplate.
 7. A separating apparatus for separating different grades ofmaterial, the separating apparatus comprising:a separation chamberhaving an upper outlet and a lower outlet; means for feeding a materialmixture to the separation chamber; a pair of first plates in the lowerportion of the separation chamber, the first plates inclining downwardlytowards the lower outlet each first plate having apertures formedtherein arranged in a first series of spaced zones along the length ofthe first plate from the lower outlet and a further apertured zonelocated between each adjacent pair of zones of the first series ofzones, the further apertured zones forming a second series of zones, theapertures in the first series of zones being inclined to the surface ofthe first plates in a direction away from the lower outlet and theapertures in the second series of zones being inclined to the surface ofthe first plates in the opposite direction, in which the ratio of thenumber of apertures in a zone of the first series of zones to the numberof apertures in a zone of the second series of zones is substantially3:1.
 8. The apparatus according to claim 7 in which the pair of firstplates are inclined at substantially 45° and the apertures in the firstand second series of zones are inclined at substantially 70° to thesurfaces of the pair of first plates.
 9. The apparatus according toclaim 7 in which the first and second series of zones extend diagonallyto the length of the pair of first plates.
 10. A separating apparatusfor separating different grades of material, the separating apparatuscomprising:a separation chamber having an upper outlet and a loweroutlet; means for feeding a material mixture to the separation chamber;a pair of first plates in the lower portion of the separation chamber,the first plates inclining downwardly towards the lower outlet, eachfirst plate having apertures formed therein arranged in a first seriesof spaced zones along the length of the first plate from the loweroutlet and a further apertured zone located between each adjacent pairof zones of the first series of zones, the further apertured zonesforming a second series of zones, the apertures in the first series ofzones being inclined to the surface of the first plates in a directionaway from the lower outlet and the apertures in the second series ofzones being inclined to the surface of the first plates in the oppositedirection; and the lower outlet is defined by a further pair ofapertured plates which extend downwardly from the lower edges of thefirst plates, the apertures in the further plates being inclinedupwardly towards the upper outlet.
 11. The apparatus according to claim10 further including separate plenum chambers for supplying fluid underpressure to the apertured first and further plates respectively so as toobtain an upward flow of fluid in the separation chamber.
 12. Theapparatus according to claim 11 further including a fan having an inletconnected to the upper outlet and an outlet connected to the plenumchambers by way of a diffuser section.
 13. The apparatus according toclaim 12 further including a valve controlled by pass ducts throughwhich fluid from the plenum chambers associated with the pair of firstplates can flow to an outlet duct connected to the upper outlet.
 14. Theapparatus according to claim 13 further including a separation unit inthe outlet duct.
 15. The apparatus according to claim 14 furtherincluding an extractor for removing part of the fluid delivered by thefan to prevent a build up of dust within the apparatus and a further fanfor replenishing the extracted fluid.
 16. The apparatus according toclaim 15 comprising a pair of further fans which supply fluid to theplenum chambers associated with the pair of first plates respectivelywhereby the pressure in the separation chamber is substantiallyatmospheric.